Sealable and peelable film structure

ABSTRACT

A sealable and peelable film, including at least (a) a core layer containing a peelable blend and (b) a pair of outer layers, at least one of which is a sealable outer layer, each independently containing a thermoplastic polymer. The peelable blend of the core layer (a) may contain (i) from 20-80 wt % of a polyethylene and (ii) from 80-20 wt % of a polyolefin incompatible with polyethylene (i), or it may contain (i) from 10-35 wt % of ethylene-α-olefin elastomer and (ii) from 90-65 wt % of propylene homopolymer. The film may also include an intermediate layer containing a propylene homopolymer, wherein the intermediate layer is positioned between the core layer containing the peelable blend and the sealable outer layer.

BACKGROUND OF THE INVENTION

[0001] The invention relates to thermoplastic film structures that aresealable and peelable, and to methods of manufacturing the same.

[0002] A peelable film structure is described in publication WO96/04178. The film structure comprises (a) a core layer comprising anolefin polymer and (b) a heat-sealable layer comprising a blend of lowdensity polyethylene (LDPE) and a material incompatible with the LDPE,such as an olefin polymer or a co- or terpolymer of ethylene, propyleneor butene. The film structure can be heat-sealed to a plastic containerto form the lid of the container, or to itself to form a package. It isdisclosed that when used with a plastic container, the film structurecan be readily peeled from the container in order to open it.

[0003] U.S. Pat. No. 5,358,792 discloses a heat-sealable compositioncomprising (a) from about 30 to about 70 wt % of a low-melting polymercomprising a very low density ethylene-based copolymer defined by adensity in the range of about 0.88 g/cm³ to about 0.915 g/cm³, a meltindex in the range of about 1.5 dg/min to about 7.5 dg/min, a molecularweight distribution (M_(w)/M_(n)) no greater than about 3.5 and (b) fromabout 70 to about 30 wt % of a propylene-based polymer.

[0004] U.S. Pat. No. 5,443,915 discloses an oriented, polyolefin filmthat has a white-opaque cold seal-receptive skin layer on one side of acore layer and a vacuum deposited metal layer on the other side of thecore layer. The cold seal-receptive polyolefin layer contains: (a) aslip agent in an amount sufficient to provide not more than about an 0.4coefficient of friction to the surface of such layer; and (b) from about10 to 40 wt % of titanium dioxide. The core layer is substantially freeof opacifying filler and/or opacifying voids. The other side of the filmis metallized to an optical density of at least 1.5, whereby the whitepigment in the sealing layer in cooperation with the metallization givesa strong white-opaque appearance to the cold seal receptive layer.

[0005] U.S. Pat. No. 5,482,780 discloses an oriented polymeric α-olefinfilm having: an isotactic propylene homopolymer core; a cold sealrelease skin layer adherent to one side of the core; and a surfacetreated cold seal receptive layer or such treated layer with a cold sealcohesive composition over the surface treatment of said layer on theother side of the core. The cold seal release skin layer comprises aslip agent and a blend of two polymers, namely, an ethylene-propylenerandom copolymer containing about 2% to 8% of ethylene in such copolymerand an ethylene-butylene copolymer containing about 0.5% to 6% ofethylene in such copolymer. The cold seal receptive layer is of anethylene-propylene random copolymer containing about 2 to 8% ofethylene.

[0006] U.S. Pat. No. 5,500,265 discloses a peelable film comprising (a)a core layer comprising an olefin polymer, (b) a skin layer on at leastone surface of the core layer, the skin layer comprising: a blend of abutylene polymer with another olefin polymer or a polymer of butyleneand at least one other olefin, and (c) a coating layer on the skinlayer.

[0007] U.S. Pat. No. 5,716,698 relates to a peelable, oriented, opaque,multilayer polyolefin film comprising at least one opaque layer and apeelable top layer. All layers of the film are essentially vacuole-free.The opaque layer contains pigments having a mean particle diameter offrom 0.01 to 1 μm.

[0008] U.S. Pat. No. 5,997,968 discloses a multilayer polyolefin filmcomprising at least three coextruded layers comprising an opaque baselayer, an intermediate layer, and an outer peelable surface layercomposed of two incompatible polyolefins, wherein the intermediate layercontains at least 80% by weight of a polyolefin having a lower meltingpoint or lower glass transition temperature than the polyolefin formingthe base layer.

[0009] U.S. Pat. No. 6,231,975 discloses a sealable film that comprises:(a) an inner layer comprising an olefin polymer; (b) a sealing layer;and (c) a separable layer positioned between the inner layer and thesealing layer, the separable layer comprising (1) ethylene-propyleneblock copolymer or (2) a blend of polyethylene and another olefin whichis incompatible with the polyethylene, specifically either (i)polypropylene homopolymer or (ii) ethylene-propylene block copolymer.

[0010] U.S. Pat. No. 6,248,442 relates to multilayer films that areheat-sealable over a broad temperature range. The '442 patent alsorelates to multilayer films that provide easy-opening and hermetic sealsto packages. The films of the '442 patent are made up of a core layercomprising linear low density polyethylene (LLDPE) and at least one skinlayer having a melting point of at least 10° C. below the core layermelting point.

[0011] There is still room for improvement, however, in the field ofsealable and peelable film structures. In particular, a need stillexists for a film structure that maximizes the advantageous combinationof (i) a sealable outer layer that seals well to itself or othersurfaces over a broad temperature range and (ii) a particular multilayerdesign that permits (a) separation of the sealed outer layer from atleast one other layer of the film and (b) the seal to be readily openedwithout creating a “z-direction” tear.

[0012] A z-direction tear disrupts the integrity of a multilayer filmwhen the film is pulled apart at the seal. A film with a z-directiontear has not simply separated at the seal line. Instead, the separation,or tear, has extended to other layers of the film. It is difficult toproperly reclose a package that has a z-direction tear, therebyhampering the ability of the package to maintain the freshness of itscontents. When z-direction tears can be eliminated, packages are easilyrefolded and sealed by simple mechanical means, such as a clip.

SUMMARY OF THE INVENTION

[0013] It is an object of the invention to provide a thermoplastic filmstructure with a sealable outer layer that seals well over a broadtemperature range.

[0014] It is another object of the invention to provide a thermoplasticfilm structure with a sealable outer layer that, when sealed, can bereadily opened without creating a z-direction tear.

[0015] It is a further object of the invention to provide athermoplastic film structure with multiple layers, including a corelayer comprising a peelable, polyolefinic blend and a sealable outerlayer that can be sealed to itself or other surfaces, wherein theparticular multilayer thermoplastic film structure permits separation ofthe sealable outer layer from at least one other layer of the film.

[0016] It is yet another object of the invention to provide both clearand opaque thermoplastic film structures.

[0017] There is provided a sealable and peelable film, including atleast (a) a core layer comprising a peelable blend comprising (i) from20-80 wt % of a polyethylene and (ii) from 80-20 wt % of a polyolefinincompatible with polyethylene (i) and (b) a pair of outer layers, atleast one of which is a sealable outer layer, each independentlycomprising a thermoplastic polymer.

[0018] There is also provided a sealable and peelable film, including atleast (a) a core layer comprising a peelable blend comprising (i) from10-35 wt % of an ethylene-α-olefin elastomer and (ii) from 90-65 wt % ofa propylene homopolymer and (b) a pair of outer layers, at least one ofwhich is a sealable outer layer, each independently comprising athermoplastic polymer.

[0019] There is also provided an opaque, sealable and peelable film,including at least (a) a cavitated first core layer comprising athermoplastic polymer and a cavitating agent; (b) a second core layercomprising a peelable blend comprising (i) from 20-80 wt % of apolyethylene and (ii) from 80-20 wt % of a polyolefin incompatible withpolyethylene (i); and (c) a pair of outer layers, at least one of whichis a sealable outer layer, each independently comprising a thermoplasticpolymer.

[0020] There is also provided an opaque, sealable and peelable film,including at least (a) a cavitated first core layer comprising athermoplastic polymer and a cavitating agent; (b) a second core layercomprising a peelable blend comprising (i) from 10-35 wt % of anethylene-α-olefin elastomer and (ii) from 90-65 wt % of a propylenehomopolymer; and (c) a pair of outer layers, at least one of which is asealable outer layer, each independently comprising a thermoplasticpolymer.

[0021] Sealable and peelable film structures according to the presentinvention may also include an intermediate layer comprising a propylenehomopolymer, wherein the intermediate layer is positioned between thecore layer comprising the peelable, polyolefinic blend and the sealableouter layer.

[0022] Once sealed, a sealable film without the present multilayerdesign is usually torn through, i.e., torn in the z-direction, to openthe seal, especially when the area where the film is sealed is strongerthan the film as a whole. With the sealable and peelable film structuresof this invention, a seal can be opened without tearing the film in thez-direction because the particular multilayer structure of the presentfilms, including a core layer comprising a peelable, polyolefinic blend,permits the seal to be separated without tearing the film in thez-direction.

[0023] Thus, a particular advantage of the present sealable and peelablefilms is that they do not compromise the desired properties of a sealmaterial, such as hot tack and seal strength, because the presentsealable outer layer(s) may use ordinary seal materials to seal thefilm, and yet the films are still peelable.

[0024] For example, a sealable and peelable film structure according tothe present invention may advantageously possess a peak crimp sealstrength between 300 g/in and 800 g/in, e.g., from 450 g/in to 750 g/in,and a ratio of plateau crimp seal strength to peak crimp seal strengthof greater than 60% and less than 100%, e.g., greater than 70% and lessthan 95%. These ranges identify a seal that is both strong and readilypeelable.

DETAILED DESCRIPTION OF THE INVENTION

[0025] The sealable and peelable film structure includes a core layercomprising a peelable, polyolefinic blend.

[0026] In general, the presence of the peelable, polyolefinic blend in acore layer means that there will be a weak bond between the core layerand adjacent layers on either side of the core layer so that stressapplied to the film structure after the film structure has been sealedwill promote destruction of the core layer and not its adjacent layers.Alternatively, the core layer comprising a peelable, polyolefinic blendmay have less cohesive strength than either of its adjacent layers,which causes the core layer to give way before either of its adjacentlayers. The term “peelable” is used herein to cover the class offilm-forming polyolefinic blends included in the core layer that allowthe layers adjacent to the core layer to be separated from the corelayer under stress as essentially integral layers.

[0027] The peelable polyolefinic blend comprises an ethylene polymer anda polyolefin incompatible with the ethylene polymer. The term“incompatible” is used in the ordinary sense both here and throughout,meaning that the ethylene polymer and the other polyolefin are twodistinct phases. The term “ethylene polymer,” as used here andthroughout, includes ethylene homo-, co- and terpolymers, including,among others, linear ethylene homopolymers, linear ethylene-α-olefincopolymers, and ethylene-α-olefin elastomers. Comonomers of the ethylenecopolymers, terpolymers, and elastomers can be C₃-C₁₂ olefins,preferably C₄-C₁₂ olefins.

[0028] More specifically, the ethylene polymer of the peelablepolyolefinic blend may be ethylene-α-olefin block copolymer,ethylene-propylene impact copolymer, high density polyethylene (HDPE),medium density polyethylene (MDPE), low density polyethylene (LDPE),linear low density polyethylene (LLDPE), very low density polyethylene(VLDPE), ethylene plastomer, ethylene-α-olefin elastomer and blendsthereof. It will be readily understood that the foregoing list ofsuitable ethylene polymers is non-exhaustive, and includes bothZiegler-Natta- and single site-catalyzed, e.g., metallocene-catalyzed,versions thereof. In preferred embodiments, the ethylene polymer of thepeelable polyolefinic blend is a linear ethylene homo- or copolymer oran ethylene-α-olefin elastomer.

[0029] LLDPE has: a melt index of from less than 1 to 10 g/10 min (asmeasured according to ASTM D1238) and a density in the range of from0.88 to 0.94 g/cm³, preferably from 0.89 to 0.92 g/cm³. It may bederived from ethylene together with other higher comonomers, such asbutene-1, hexene-1 or octene-1.

[0030] HDPE is a substantially linear polyolefin having a density of,for example, from about 0.941 g/cm³ or higher, e.g., from about 0.952g/cm³ to about 0.970 g/cm³, and a melting point of, for example, fromabout 266° F. to about 299° F. (from about 130° C. to about 148° C.).

[0031] MDPE has a density in the range of from about 0.926 g/cm³ toabout 0.940 g/cm³.

[0032] LDPE has a density in the range of from 0.90 g/cm³ to 0.94 g/cm³,e.g., from 0.910 g/cm³ to 0.926 g/cm³, and a melt index of from lessthan 1 to 10 g/10 min (as measured according to ASTM D1238). LDPE may bederived solely from ethylene in a high pressure polymerization. LLDPE ismade from ethylene together with a comonomer, including but not limitedto higher olefin comonomers containing 4 to 12 carbon atoms, e.g.,butene-1, hexene-1, or octene-1, e.g., in a gas phase linear low densitypolyethylene (LLDPE) process or in a solution LLDPE process usingZiegler-Natta or single-site, e.g., metallocene, catalysts. When LDPEhas been polymerized at high pressure, it is typically referred to ashigh-pressure polyethylene or branch polyethylene.

[0033] VLDPE, which is sometimes referred to as ultra low densitypolyethylene (ULDPE), is a very low density polyethylene that has adensity at or below 0.915 g/cm³, e.g., from about 0.86 to about 0.915g/cm³, a melt index in the range of about 1.5 dg/min to about 7.5dg/min, and a melting point in the range of about 60° C. to about 115°C., measured as DSC peak T_(m). VLDPE is typically produced in a highpressure, peroxide-catalyzed reaction or in a solution process. Whenproduced using a metallocene or other single-site catalyst, VLDPE iscommonly referred to as a type of plastomer.

[0034] Ethylene-propylene impact copolymer may be produced in tworeactors. A first reactor generates, e.g., isotactic propylenehomopolymer. In a second reactor, ethylene and propylene are polymerizedto create an ethylene-propylene elastomer. The isotactic propylenehomopolymer of the first reactor may be transferred to theethylene-propylene elastomer of the second reactor, wherein theethylene-propylene elastomer is dispersed in the isotactic propylenehomopolymer phase at a ratio of from 60-95% by weight of isotacticpropylene homopolymer and from 5-40% by weight of ethylene-propyleneelastomer, each based on the total weight of the final impact copolymer.

[0035] When the peelable polyolefinic blend comprises ethylene-α-olefinblock copolymer, the block copolymer comprises from about 3 to about 25wt % ethylene, based on the total weight of the block copolymer. Theterm “block” is used in the ordinary sense both here and throughout,meaning a polymer made up of alternating sections of ethylene orpolyethylene and sections of a different olefin. For example, in anethylene-propylene block copolymer, the ethylene or polyethylenesections alternate with propylene or polypropylene sections.

[0036] When the peelable polyolefinic blend comprises ethylene-α-olefinelastomer, the elastomer comprises from 50 mol % to 80 mol % ethylene,based on the total moles of the elastomer. The α-olefin of theethylene-α-olefin elastomer may be a C₃ to C₁₂ olefin; preferably, theα-olefin is propylene.

[0037] In addition, ethylene-α-olefin elastomer may be added as asupplemental component to a core layer comprising a peelablepolyolefinic blend in instances where the peelable polyolefinic blenditself does not comprise an ethylene-α-olefin elastomer. For example, acore layer comprising a peelable polyolefinic blend may be supplementedwith from about 1 to about 5 wt % of an ethylene-α-olefin elastomer. Theaddition of from about 1 to about 5 wt % of an ethylene-α-olefinelastomer to a core layer comprising a peelable polyolefinic blendenhances the overall tear resistance of the sealable and peelable film.

[0038] Commercially available polyethylenes suitable for the peelablepolyolefinic blend include an ethylene-propylene block copolymer sold byHimont as “8523”; a LLDPE sold by Exxon as “LL3001”; ametallocene-catalyzed plastomer ethylene-hexene copolymer sold by Exxonas “SLP 9045”; a HDPE sold by Oxychem as “M6211”; a LDPE sold by Chevronas “PE1019”; a metallocene-catalyzed polyethylene sold by Exxon as“Exact 2009”; a LLDPE sold by Eastman Chemical as “Eastman L72108x”; anethylene-propylene elastomer that has 60 mol % ethylene sold by Exxon as“Exxelor PE901”; and a LLDPE sold by Dow Chemical as “Dowlex 2038.”

[0039] Although any polyolefin incompatible with polyethylene may bechosen for the peelable polyolefinic blend, in a preferred embodiment, apropylene polymer is employed, and in a particularly preferredembodiment, a propylene homopolymer is employed. The term “propylenepolymer,” as used here and throughout, includes propylene homo-, co- andterpolymers. The particularly preferred propylene homopolymer may bepredominantly isotactic, syndiotactic or atactic, and may include ablend of any of the foregoing forms of propylene homopolymer. Thepropylene homopolymer may be produced by using Ziegler-Natta or singlesite, e.g., metallocene, catalysts.

[0040] For example, the particularly preferred propylene homopolymer maybe an isotactic propylene homopolymer having (i) an isotacticity of fromabout 85 to 99%, (ii) a melting point of from about 311° F. (155° C.) toabout 329° F. (165° C.), and (iii) a melt flow rate of from about 0.5 toabout 15 g/10 minutes (as measured according to ASTM D1238).

[0041] Propylene homopolymers available developmentally or commerciallyand suitable for the peelable polyolefinic blend includemetallocene-catalyzed propylene homopolymers, such as EOD 96-21 and EOD97-09, from Fina Oil and Chemical Co., EXPP-129, from ExxonMobilChemical Co., Novalen M, from BASF GmbH., and Ziegler-Natta-catalyzedpropylene homopolymers, such as “Fina 3371” sold by Fina Oil andChemical Company.

[0042] The respective amounts present in the peelable polyolefinic blendof (i) ethylene polymer and (ii) polyolefin incompatible with theethylene polymer may vary over a wide range. For example, the peelablepolyolefinic blend may comprise from about 20 to about 80 wt % of (i)ethylene polymer and from about 80 to about 20 wt % of (ii) incompatiblepolyolefin, each based on the total weight of the peelable polyolefinicblend. In a preferred embodiment, the peelable polyolefinic blendcomprises from about 20 to about 40 wt % of (i) ethylene polymer andfrom about 80 to about 60 wt % of (ii) incompatible polyolefin, eachbased on the total weight of the peelable polyolefinic blend.

[0043] In the particular case where the ethylene polymer (i) of thepeelable polyolefinic blend is an ethylene-α-olefin elastomer, thepeelable polyolefinic blend may comprise from about 10 to about 35 wt %of ethylene-α-olefin elastomer and from about 90 to about 65 wt % ofpropylene homopolymer. Preferably, the peelable polyolefinic blendcomprises from about 10 to about 20 wt % of ethylene-α-olefin elastomerand from about 90 to about 80 wt % of propylene homopolymer.

[0044] The sealable and peelable film structure may be clear or opaque.

[0045] The thickness of the core layer comprising a peelable,polyolefinic blend may be important in some embodiments. For example,the polyolefinic blend-containing core layer of a clear film structureis preferably from 7.5 to 70 μm thick, with a total film thicknessranging from 11 to 100 μm, e.g., from 11 to 75 μm thick. On the otherhand, the polyolefinic blend-containing core layer of an opaque filmstructure is preferably from 7.5 to 15 μm thick, with a cavitated corelayer preferably from 7.5 to 55 μm thick, a total two core layerthickness of preferably from 15 to 70 μm, and a total film thickness offrom 17.5 to 100 μm, e.g., from 17.5 to 75 μm thick.

[0046] For clear embodiments, the layers of the sealable and peelablefilm structure, including the core layer comprising a peelablepolyolefinic blend described in detail above, and other layers of thefilm structure yet to be described in detail, are devoid of anycavitating agent or opacifying agent. In addition, the respectiveamounts of (i) ethylene polymer and (ii) polyolefin incompatible withthe ethylene polymer present in the peelable polyolefinic blend may bespecifically selected to meet optimal optical clarity objectives throughroutine experimentation.

[0047] For opaque embodiments, a cavitating agent and/or an opacifyingagent may be added to any one or more of the layers of the filmstructure. In preferred opaque embodiments, however, the core layercomprising a peelable polyolefinic blend is devoid of any cavitatingagent or opacifying agent, and the sealable and peelable film structurederives its opacity from one or more cavitated core layers. For example,in a preferred opaque embodiment, the sealable and peelable filmstructure may comprise a cavitated first core layer and a non-cavitatedsecond core layer comprising the peelable polyolefinic blend, i.e., thecore layer previously described in detail.

[0048] A cavitated core layer according to the invention comprises afilm-forming, thermoplastic polymer. The film-forming, thermoplasticpolymer of the cavitated core layer is not particularly limited, and mayinclude any such polymer known in the art, or any such blend ofpolymers. Preferably, the thermoplastic polymer comprises a film-formingpolyolefin, be it either Ziegler-Natta- or single site-catalyzed. Mostpreferably, the thermoplastic polymer comprises a film-forming ethylenepolymer or propylene polymer.

[0049] In general, if the thermoplastic polymer is a propylene polymer,it is predominantly isotactic, syndiotactic or atactic. The propylenepolymer, however, may comprise greater than about 80 wt % of isotacticpolypropylene, based on the entire weight of the propylene polymer, orgreater than about 80 wt % of syndiotactic polypropylene, based on theentire weight of the propylene polymer. As a particular example, thethermoplastic polymer of the cavitated core layer may comprise anisotactic propylene homopolymer that has (i) an isotacticity of fromabout 85 to 99%, (ii) a melting point of from about 311° F. (155° C.) toabout 329° F. (165° C.), and (iii) a melt flow rate of from about 0.5 toabout 15 g/10 minutes (as measured according to ASTM D1238). On theother hand, if the thermoplastic polymer of the cavitated core layer isan ethylene polymer, it will typically be high density polyethylene(HDPE).

[0050] A cavitated core layer according to the invention also comprisesa cavitating agent(s) dispersed within the film-forming thermoplasticpolymer before extrusion and orientation. A suitable cavitating agent(s)includes any organic or inorganic material that is incompatible with,and has a higher melting point than, the film-forming thermoplasticpolymer of the cavitated core layer, at least at the orientationtemperature.

[0051] For example, the cavitating agent(s) may be any of thosedescribed in U.S. Pat. Nos. 4,377,616 and 4,632,869, the entiredisclosures of which are incorporated herein by reference. Specificexamples of the cavitating agent(s) include polybutyleneterephthalate(PBT), nylon, ethylene-norborene, cyclic olefin copolymer, syndiotacticpolystyrene, syndiotactic polystyrene copolymer, a solid preformed glasssphere, a hollow preformed glass sphere, a metal bead, a metal sphere, aceramic sphere, calcium carbonate (CaCO₃), and combinations thereof.When a cavitated core layer comprising a cavitating agent(s) issubjected to uniaxial or biaxial orientation, a cavity forms, providinga film having an opaque appearance.

[0052] Suitable cavitating agents for the invention may be availablecommercially. For example, PBT1300A, available from Ticona, is apolybutyleneterephthalate (PBT). When mixed with molten polypropylene,e.g., Fina 3371 propylene homopolymer, it forms particles of a sphericalshape that have a mean particle size of from 1 to 3 μm. 6080HD,available from Schulman, is a masterbatch of high density polyethylene(HDPE) and calcium carbonate (CaCO₃). 6080HD is 60 wt % CaCO₃ and 40 wt% HDPE.

[0053] In general, the particle size of the cavitating agent(s) may be,for example, from about 0.1 micron to about 10 microns, more preferablyfrom about 0.2 micron to about 2 microns. The cavitating agent(s) mayalso be of any desired shape. For example, the cavitating agent(s) maybe substantially spherical. The cavitating agent(s) may be present inthe cavitated core layer in an amount of less than 30 wt %, for examplefrom 2 wt % to 20 wt %, e.g., from 5 wt % to 10 wt %, based on the totalweight of the cavitated core layer.

[0054] The cavitating agent(s) may be dispersed within the film-formingthermoplastic polymer by blending the cavitating agent(s) and thethermoplastic polymer at a temperature above the melting point of thethermoplastic polymer. The blending may take place in, e.g., anextruder, including a single-screw extruder and a co-rotating,intermeshing twin screw extruder.

[0055] The cavitated core layer may also comprise an opacifying agent.Examples of the opacifying agent include iron oxide, carbon black,titanium dioxide, talc, and combinations thereof. The opacifying agentmay be present in the cavitated core layer in an amount of from 1 to 25wt %, for example from 1 to 8 wt %, e.g., from about 2 to about 4 wt %,based on the total weight of the cavitated core layer. Aluminum isanother example of an opacifying agent that may be used. Aluminum may beincluded in the cavitated core layer as an opacifying agent in an amountof from 0.01 to 1.0 wt %, e.g., from about 0.25 to about 0.85 wt %,based on the total weight of the cavitated core layer.

[0056] The sealable and peelable film structure comprises a pair ofouter layers. At least one of the outer layers is a sealable outerlayer.

[0057] In general, the sealable outer layer comprises a coextrudable orextrusion-coatable material that forms a seal, either with itself or toother surfaces, upon application of elevated temperatures and, at leastslight, pressure. Examples of thermoplastic materials which can be usedfor the sealable outer layer include olefinic homo-, co- andterpolymers. The olefinic monomers can comprise 2 to 8 carbon atoms.

[0058] Specific examples of thermoplastic materials suitable for thesealable outer layer include ethylene-propylene random copolymer,ethylene-butene-1 copolymer, ethylene-propylene-butene-1 terpolymer,propylene-butene copolymer, low density polyethylene (LDPE) orhigh-pressure polyethylene, linear low density polyethylene (LLDPE),very low density polyethylene (VLDPE), single-site metallocene-catalyzedethylene copolymer, including single-site metallocene-catalyzedethylene-hexene copolymer, single-site metallocene-catalyzedethylene-butene copolymer, and single-site metallocene-catalyzedethylene-octene copolymer, single-site metallocene-catalyzed polymerknown by the term plastomer, ethylene-methacrylic acid copolymer,ethylene-vinyl acetate copolymer, and ionomer resin. A blend of any twoor more of the foregoing thermoplastic materials is also contemplated,such as a blend of the plastomer and ethylene-butene copolymer.

[0059] As mentioned, one outer layer may be a sealable outer layer, orboth outer layers may be sealable outer layers. In the case where bothouter layers are sealable outer layers, the materials employed in eachouter layer may be the same or different. In the case where only oneouter layer is a sealable outer layer, the other outer layer, i.e., thenon-sealable outer layer, may comprise a film-forming, thermoplasticpolymer.

[0060] The film-forming, thermoplastic polymer of the non-sealable outerlayer is not particularly limited, and may include any such polymerknown in the art, or any such blend of polymers. Preferably, thethermoplastic polymer comprises a film-forming polyolefin, be it eitherZiegler-Natta- or single-site metallocene-catalyzed. Most preferably,the thermoplastic polymer comprises a film-forming ethylene polymer orpropylene polymer. For example, the thermoplastic polymer of thenon-sealable outer layer may comprise an isotactic propylenehomopolymer, a propylene copolymer or high density polyethylene (HDPE).

[0061] To broadly summarize the invention as described thus far, thereare provided clear, sealable and peelable film structure embodiments andopaque, sealable and peelable film structure embodiments. In the clearembodiments, the film structure comprises a core layer comprising apeelable, polyolefinic blend and a pair of outer layers. In the opaqueembodiments, the film structure preferably comprises a non-cavitatedcore layer comprising a peelable, polyolefinic blend, one or morecavitated core layers, and a pair of outer layers. For both the clearand opaque embodiments, at least one of the outer layers is a sealableouter layer The individual layers in the opaque embodiments arepreferably arranged in a manner such that the core layer comprising apeelable, polyolefinic blend is positioned between the sealable outerlayer and the one or more cavitated core layers.

[0062] Whether clear or opaque, sealable and peelable film structuresaccording to the invention may additionally comprise one or moreintermediate layers. For example, a clear, sealable and peelable filmstructure may be prepared that has one or more intermediate layerspositioned (i) between the core layer and a first outer layer and/or(ii) between the core layer and a second outer layer. Likewise, anopaque, sealable and peelable film structure may be prepared that hasone or more intermediate layers positioned (i) between a core layer anda first outer layer and/or (ii) between a core layer and a second outerlayer and/or (iii) between the core layer comprising a peelablepolyolefinic blend and the one or more cavitated core layers and/or (iv)between two cavitated core layers for embodiments where there is morethan one cavitated core layer.

[0063] Although the presence of one or more intermediate layers inopaque embodiments may mean that the core layer comprising a peelable,polyolefinic blend is no longer positioned directly between, i.e.,directly adjacent to, the sealable outer layer and the one or morecavitated core layers, it will be readily understood that the core layercomprising a peelable, polyolefinic blend is still preferablypositioned, in a general sense, i.e., indirectly, between the sealableouter layer and the one or more cavitated core layers.

[0064] An intermediate layer according to the invention comprises afilm-forming, thermoplastic polymer. The film-forming, thermoplasticpolymer of the intermediate layer is not particularly limited, and mayinclude any such polymer known in the art, or any such blend ofpolymers. Preferably, the thermoplastic polymer comprises a film-formingpolyolefin, be it either Ziegler-Natta- or single-sitemetallocene-catalyzed. Most preferably, the thermoplastic polymercomprises a film-forming ethylene polymer or propylene polymer.

[0065] In general, if the thermoplastic polymer is a propylene polymer,it is predominantly isotactic, syndiotactic or atactic. The propylenepolymer, however, may comprise greater than about 80 wt % of isotacticpolypropylene, based on the entire weight of the propylene polymer, orgreater than about 80 wt % of syndiotactic polypropylene, based on theentire weight of the propylene polymer. As a particular example, thethermoplastic polymer of the intermediate layer may comprise anisotactic propylene homopolymer that has (i) an isotacticity of fromabout 89 to 99%, (ii) a melting point of from about 311° F. (155° C.) toabout 329° F. (165° C.), and (iii) a melt flow rate of from about 0.5 toabout 15 g/10 minutes (as measured according to ASTM D1238). On theother hand, if the thermoplastic polymer of the intermediate layer is anethylene polymer, it will typically be high density polyethylene (HDPE).

[0066] According to a particularly preferred embodiment, a clear,sealable and peelable film structure comprises an intermediate layercomprising a propylene homopolymer between the core layer comprising apeelable, polyolefinic blend and the sealable outer layer. The inventorshave found that positioning an intermediate layer comprising a propylenehomopolymer between the core layer and sealable outer layer maximizesthe peelability of the layer(s) on the side of the core layer oppositethe sealable outer layer from the sealable outer layer withoutsubstantially destroying either the layer(s) or the sealable outerlayer.

[0067] Although it is not preferred, an intermediate layer comprising apropylene homopolymer may also be positioned between the core layercomprising the peelable, polyolefinic blend and the sealable outer layerin opaque embodiments of the invention.

[0068] The thickness of an intermediate layer may be important in someembodiments. For example, the thickness of an intermediate layerpositioned between a core layer comprising a peelable, polyolefinicblend and a sealable outer layer is preferably from 1 to 3 μm in bothclear and opaque embodiments. In this regard, an intermediate layerpositioned between a core layer comprising a peelable, polyolefinicblend and a sealable outer layer may improve the optical gloss andclarity of a clear film and the optical gloss of an opaque film. If theintermediate layer in these applications is greater than 3 μm, thepeel-separation surface of the sample after the peel test is not clean,i.e., some fiber tails are present, even if it is still a peelable seal.If the intermediate layer thickness is below 1 μm in these applicationsis less than 1 μm, the optical property improvement is not effective dueto film processing difficulty.

[0069] In order to modify or enhance certain properties of the sealableand peelable film structure for specific end uses, it is possible forone or more of the layers to contain appropriate additives in effectiveamounts. The term “effective amount,” as used herein and throughout, isan amount sufficient to achieve the desired effect, e.g., anantiblocking effect for antiblock additives or an antistatic effect forantistatic additives. Examples of suitable additives may include, butare not limited to, waxes, pigments, colorants, antioxidants,antiozonants, antifogs, antistats, slip additives, antiblock additives,fillers such as diatomaceous earth and carbon black, and combinationsthereof.

[0070] One or more barrier additives may be employed in one or more ofthe layers of the invention. Suitable barrier additives include, but arenot limited to, low molecular weight resins, such as hydrocarbon resins,and more particularly, petroleum resins, styrene resins, cyclopentadieneresins, terpene resins, and alicyclic resins. These types of barrieradditives are further described in U.S. Pat. No. 5,254,394, which isincorporated herein by reference.

[0071] Typically, a commercially available intensive mixer, such asthose of the Bolling- or Banbury-type, may be employed in mixing aconcentrate of the additive material and the polymer(s) of the selectedlayer until there is a uniform dispersion of the additive material inthe polymer or polymer blend.

[0072] The sealable and peelable film structure may be surface-treatedon the outer surfaces of one or both outer layers. The outer surface(s)may be surface-treated during or after orientation. The surfacetreatment can be carried out by any method, including, but not limitedto, corona discharge treatment, flame treatment, and plasma treatment.The outer surface(s) may be treated to a surface tension level of atleast about 35 dynes/cm, e.g. from about 38 to 55 dynes/cm, inaccordance with ASTM Standard D2578-84.

[0073] As described earlier, at least one of the outer layers of thesealable and peelable film structure is a sealable outer layer. Incertain embodiments, one outer layer will be a sealable outer layer anda second outer layer is metallized via the application thereto of a thinlayer of metal.

[0074] The metallization may be by vacuum deposition, or any othermetallization technique, such as electroplating or sputtering. The metalmay be aluminum, or any other metal capable of being vacuum deposited,electroplated, or sputtered, such as, for example, gold, zinc, copper,or silver.

[0075] Typically, a metal layer is applied to an optical density of from1.5 to 5.0, e.g., from 1.8 to 2.6. Optical density is a measure of theabsorption of visual light, and is determined by standard techniques. Tocalculate optical density, a commercial densitometer may be used, suchas a Macbeth model TD 932, Tobias Densitometer model TDX or Macbethmodel TD903. The densitometer is set to zero with no film specimen. Afilm specimen is placed over the aperture plate of the densitometer withthe test surface facing upwards. The probe arm is pressed down and theresulting optical density value is recorded.

[0076] The sealable and peelable film structure may have a coating layerapplied to the outer surfaces of one or both of its outer layers. Forexample, a coating may be applied to the sealable outer layer tofacilitate sealing of the film to itself or to another film surface.Preferably, any coating applied onto the outer surface of a metallizedouter layer is applied after the outer surface has been metallized,i.e., the coating is actually applied onto the metal layer that has beendeposited on the outer layer. Examples of suitable coatings include, butare not limited to, ethylene-acrylic acid copolymer (EAA),ethylene-methacrylic acid copolymer (EMA), alkyl acrylate copolymer,acrylonitrile, polyvinylidene chloride (PVdC), polyvinyl alcohol (PVOH),and urethane copolymer.

[0077] The sealable and peelable film structure may be manufacturedusing film technology that is well-known to those skilled in the art.For example, melts corresponding to the individual layers of the filmstructure may be prepared. The melts may be cast-extruded or coextrudedinto a sheet using a flat die or blown-extruded or coextruded using atubular die. The sheets may then be oriented either uniaxially orbiaxially by known stretching techniques.

[0078] In a particular embodiment, the outer layers are coextruded withthe other layers of the film structure. In another embodiment, only oneof the outer layers is coextruded with the other layers of the filmstructure. The other outer layer is extrusion-coated onto an outersurface of the film structure. In yet another embodiment, each outerlayer is extrusion-coated onto a respective outer surface of the filmstructure. Regarding extrusion-coating, it may be performed after thefilm has been oriented or in the middle of the orientation process. Forexample, after orienting a coextruded sheet in the machine direction, anouter layer may be extrusion-coated onto an outer surface thereof,followed by transverse direction orientation.

[0079] The following examples illustrate the present invention. For eachexample, a coextruded, biaxially oriented film was prepared using therespective olefinic polymer resins described below. Specifically, theparticular polymer resins were melted at a temperature ranging fromabout 245 to about 290° C., the molten polymers were coextruded througha slot die in sheet form, and the coextruded sheet was oriented(sequentially) in the machine direction (about 3 to about 8 times atabout 100° C.) and in the transverse direction (about 5 to about 12times at about 160° C.).

[0080] The peelability for each film in Examples 1-9 was tested asfollows. The film was sealed by crimp-sealing the seal layer (layer C inExamples 1-3; layer D in Examples 4-9) to itself. Then a tester tried topull the seal apart. For each of the films in Examples 1-9, the testerwas able to separate the seal without severing the film, i.e., withoutcreating a z-direction tear, indicating the effective performance of thepeelable film structure.

[0081] For the films of Examples 4-9, the film's sealability was testedto confirm that the seal strength of the peelable film structure was notadversely impacted. Specifically, the seal strength for each of thefilms of Examples 4-9 was evaluated by crimp-sealing the seal layer toitself at 260° F., 20 psi pressure, and ¾ second dwell time. Thecrimp-sealed sample was cut into 1 inch width and peeled apart at a 180°angle by an Instron Tensile machine at the speed of 0.3 m/min. The peelforce versus separation distance was recorded into a chart by acomputer, and the peak crimp seal strength and average peel propagationstrength, i.e., the plateau crimp seal strength, were measured (as shownin Tables 1 and 2).

EXAMPLE 1

[0082] A three-layer clear film with an A/B/C structure was prepared,wherein layer A is a skin layer about 1 μm thick comprising a propylenehomopolymer, layer B is a peelable core layer about 20 μm thickcomprising a blend of 70 wt % propylene homopolymer and 30 wt %metallocene-catalyzed polyethylene, and layer C is a sealable skin layerabout 1 μm thick comprising an ethylene-propylene-butene terpolymer. Thefilm was coextruded and biaxially oriented.

[0083] The tester succeeded in pulling apart the seal without creating az-direction tear, which confirmed that the film was a peelable film.

EXAMPLE 2

[0084] A three-layer clear film with an A/B/C structure was prepared,wherein layer A is a skin layer about 1 μm thick comprising a propylenehomopolymer, layer B is a peelable core layer about 20 μm thickcomprising a blend of 70 wt % propylene homopolymer and 30 wt %metallocene-catalyzed polyethylene, and layer C is a sealable skin layerabout 1 μm thick comprising a metallocene-catalyzed polyethylene. Thefilm was coextruded and biaxially oriented.

[0085] The tester succeeded in pulling apart the seal without creating az-direction tear, which confirmed that the film was a peelable film.

EXAMPLE 3

[0086] A three-layer opaque film with an B1/B2/C structure was prepared,wherein layer B1 is a cavitated core layer about 18 μm thick comprising82 wt % of propylene homopolymer and 18 wt % of calcium carbonate(CaCO₃), layer B2 is a peelable core layer about 7.5 μm thick comprisinga blend of 70 wt % propylene homopolymer and 30 wt %metallocene-catalyzed polyethylene, and layer C is a sealable skin layerabout 1 μm thick comprising an ethylene-propylene-butene terpolymer. Thefilm was coextruded and biaxially oriented.

[0087] The tester succeeded in pulling apart the seal without creating az-direction tear, which confirmed that the film was a peelable film.

EXAMPLE 4

[0088] A four-layer clear film with an A/B/C/D structure was prepared,wherein layer A is a skin layer about 1.75 μm thick comprising Fina 3371propylene homopolymer, layer B is a peelable core layer about 15 μmthick comprising a blend of 70 wt % Fina 3371 propylene homopolymer and30 wt % Eastman L72108x linear low density polyethylene (LLDPE), layer Cis an intermediate layer about 2.5 μm thick comprising Fina 3371propylene homopolymer, and layer D is a sealable skin layer about 0.75μm thick comprising Chisso 7701 ethylene-propylene-butene-1 terpolymerfrom Chisso Company, Japan. The film was coextruded and biaxiallyoriented.

[0089] The tester succeeded in pulling apart the seal without creating az-direction tear, which confirmed that the film was a peelable film. Thegloss, haze, and seal strength of the film were measured, and theresults are presented at Table 1 below.

EXAMPLE 5

[0090] A four-layer clear film with an A/B/C/D structure was prepared,wherein layer A is a skin layer about 4.25 μm thick comprising Fina 3371propylene homopolymer, layer B is a peelable core layer about 15 μmthick comprising a blend of 70 wt % Fina 3371 propylene homopolymer and30 wt % Eastman L72108x linear low density polyethylene (LLDPE), layer Cis an intermediate layer about 2.5 μm thick comprising Fina 3371propylene homopolymer, and layer D is a sealable skin layer about 0.75μm thick comprising Chisso 7701 ethylene-propylene-butene-1 terpolymer.The film was coextruded and biaxially oriented.

[0091] The tester succeeded in pulling apart the seal without creating az-direction tear, which confirmed that the film was a peelable film. Thegloss, haze, and seal strength of the film were measured, and theresults are presented at Table 1 below.

EXAMPLE 6

[0092] A four-layer clear film with an A/B/C/D structure was prepared,wherein layer A is a skin layer about 1.75 μm thick comprising Fina 3371propylene homopolymer, layer B is a peelable core layer about 15 μmthick comprising a blend of 70 wt % Fina 3371 propylene homopolymer and30 wt % Dowlex 2038 linear low density polyethylene (LLDPE), layer C isan intermediate layer about 2.5 μm thick comprising Fina 3371 propylenehomopolymer, and layer D is a sealable skin layer about 0.75 μm thickcomprising Chisso 7701 ethylene-propylene-butene-1 terpolymer. The filmwas coextruded and biaxially oriented.

[0093] The tester succeeded in pulling apart the seal without creating az-direction tear, which confirmed that the film was a peelable film. Thegloss, haze, and seal strength of the film were measured, and theresults are presented at Table 1 below.

EXAMPLE 7

[0094] A four-layer clear film with an A/B/C/D structure was prepared,wherein layer A is a skin layer about 1.25 μm thick comprising Fina 3371propylene homopolymer, layer B is a peelable core layer about 15 μmthick comprising a blend of 70 wt % Fina 3371 propylene homopolymer and30 wt % Eastman L72108x linear low density polyethylene (LLDPE), layer Cis an intermediate layer about 2.5 μm thick comprising Fina 3371propylene homopolymer, and layer D is a sealable skin layer about 1.25μm thick comprising a blend of 30 wt % Chisso 7701ethylene-propylene-butene-1 terpolymer and 70 wt % Elvax 3128ethylene-vinyl acetate (EVA). The film was coextruded and biaxiallyoriented.

[0095] The tester succeeded in pulling apart the seal without creating az-direction tear, which confirmed that the film was a peelable film. Thegloss, haze, and seal strength of the film were measured, and theresults are presented at Table 1 below.

EXAMPLE 7A

[0096] A four-layer clear film with an A/B/C/D structure was prepared,wherein layer A is a skin layer about 1.25 μm thick comprising Fina 3371propylene homopolymer, layer B is a peelable core layer about 15 μmthick comprising a blend of 90 wt % Fina 3371 propylene homopolymer and10 wt % Exxon Exxelor PE901 ethylene-propylene elastomer with 60 mol %ethylene, layer C is an intermediate layer about 2 μm thick comprisingFina 3371 propylene homopolymer, and layer D is a sealable skin layerabout 1.25 μm thick comprising Chisso 7701 ethylene-propylene-butene-1terpolymer. The film was coextruded and biaxially oriented.

[0097] The tester succeeded in pulling apart the seal without creating aZ-direction tear, which confirmed that the film was a peelable film. Thegloss, haze, and seal strength of the film were measured, and theresults are presented at Table 1 below. TABLE 1 PEELABLE, CLEAR FILMDATA Crimp Seal @ 260° F. Plateau Ex. Gloss¹ (%) Haze² (%) (g/in) Peak(g/in) Plateau/Peak 4 89.7 1.9 423 458 92% 5 89.5 1.9 432 492 88% 6 90.11.5 433 494 88% 7 68.5 5.6 363 486 75% 7A 84.1 3.0 574 639 90%

EXAMPLE 8

[0098] A four-layer opaque film with an A/B/C/D structure was prepared,wherein layer A is a skin layer about 3.75 μm thick comprising Fina 3371propylene homopolymer, layer B is a cavitated core layer about 17.5 μmthick comprising 94 wt % Fina 3371 propylene homopolymer and 6 wt %Ticona PBT1300A polybutylene terephthalate (PBT), layer C is a peelablecore layer about 7.5 μm thick comprising 70 wt % Fina 3371 propylenehomopolymer and 30 wt % Dowlex 2038 linear low density polyethylene(LLDPE), and layer D is a sealable skin layer about 0.75 μm thickcomprising Chisso 7701 ethylene-propylene-butene-1 terpolymer. The filmwas coextruded and biaxially oriented.

[0099] The tester succeeded in pulling apart the seal without creating az-direction tear, which confirmed that the film was a peelable film. Thelight transmission and seal strength of the film were measured, and theresults are presented at Table 2 below.

EXAMPLE 9

[0100] A four-layer opaque film with an A/B/C/D structure was prepared,wherein layer A is a skin layer about 3.75 μm thick comprising Fina 3371propylene homopolymer, layer B is a cavitated core layer about 17.5 μmthick comprising 80 wt % Fina 3371 propylene homopolymer and 20 wt % ofSchulman 6080HD calcium carbonate (CaCO₃) masterbatch, layer C is apeelable core layer about 7.5 μm thick comprising 70 wt % Fina 3371propylene homopolymer and 30 wt % Eastman L72108x linear low densitypolyethylene (LLDPE), and layer D is a sealable skin layer about 0.75 μmthick comprising Chisso 7701 ethylene-propylene-butene-1 terpolymer. Thefilm was coextruded and biaxially oriented.

[0101] The tester succeeded in pulling apart the seal without creating az-direction tear, which confirmed that the film was a peelable film. Thelight transmission and seal strength of the film were measured, and theresults are presented at Table 2 below. TABLE 2 PEELABLE, OPAQUE FILMDATA Light Crimp Seal @ 260° F. Ex. transmission¹ (%) Plateau (g/in)Peak (g/in) Plateau/Peak 8 27.4 641 737 87% 9 34.7 517 584 89%

What is claimed is:
 1. An oriented sealable and peelable film,comprising: (a) a first outer layer comprising a thermoplastic polymer;(b) a core layer comprising a peelable blend comprising (i) from 20-80wt % of a polyethylene and (ii) from 80-20 wt % of a polyolefinincompatible with polyethylene (i) of core layer (b); and (c) a sealablesecond outer layer comprising a thermoplastic polymer, wherein sealablesecond outer layer (c) is positioned such that core layer (b) is betweenfirst outer layer (a) and sealable second outer layer (c).
 2. Anoriented sealable and peelable film, comprising: (a) a first outer layercomprising a thermoplastic polymer; (b) a core layer comprising apeelable blend comprising (i) from 20-80 wt % of a polyethylene and (ii)from 80-20 wt % of a polyolefin incompatible with polyethylene (i) ofcore layer (b); (c) an intermediate layer comprising a propylenehomopolymer, wherein intermediate layer (c) is positioned such that corelayer (b) is between first outer layer (a) and intermediate layer (c);and (d) a sealable second outer layer comprising a thermoplasticpolymer, wherein sealable second outer layer (d) is positioned such thatintermediate layer (c) is between core layer (b) and sealable secondouter layer (d).
 3. The film of claim 2, wherein the polyethylene (i) ofcore layer (b) is selected from the group consisting of linear ethylenehomopolymer, linear ethylene-α-olefin copolymer, single-sitemetallocene-catalyzed ethylene homopolymer, single-sitemetallocene-catalyzed ethylene-α-olefin copolymer, ethylene-α-olefinblock copolymer, ethylene-propylene impact copolymer, and blendsthereof, and wherein the α-olefin of the linear ethylene-α-olefincopolymer and the α-olefin of the single-site metallocene-catalyzedethylene-α-olefin copolymer are independently selected from the groupconsisting of C₄-C₁₂ α-olefins.
 4. The film of claim 2, wherein thepolyethylene (i) of core layer (b) is ethylene-hexene copolymer.
 5. Thefilm of claim 2, wherein the polyethylene (i) of core layer (b) isethylene-octene copolymer.
 6. The film of claim 2, wherein thepolyolefin (ii) incompatible with the polyethylene (i) of core layer (b)is propylene homopolymer.
 7. The film of claim 2, wherein thethermoplastic polymer of sealable second outer layer (d) is selectedfrom the group consisting of ethylene-propylene random copolymer,ethylene-propylene-butene-1 terpolymer, propylene-butene copolymer, lowdensity polyethylene (LDPE), linear ethylene-α-olefin copolymer,single-site metallocene-catalyzed ethylene-α-olefin copolymer,ethylene-methacrylic acid copolymer, ethylene-vinyl acetate copolymer,ionomer, and blends thereof.
 8. The film of claim 2, wherein thethermoplastic polymer of first outer layer (a) is a propylenehomopolymer or a propylene copolymer.
 9. The film of claim 2, whereincore layer (b) comprises a peelable blend comprising (i) from 20-40 wt %of a polyethylene selected from the group consisting of high densitypolyethylene (HDPE), ethylene-butene copolymer, ethylene-pentenecopolymer, ethylene-hexene copolymer, ethylene-heptene copolymer,ethylene-octene copolymer, single-site metallocene-catalyzed ethylenehomopolymer, single-site metallocene-catalyzed ethylene-hexenecopolymer, single-site metallocene-catalyzed ethylene-octene copolymer,single-site metallocene-catalyzed plastomer, ethylene-α-olefin blockcopolymer, ethylene-propylene impact copolymer, and blends thereof and(ii) from 80-60 wt % of propylene homopolymer.
 10. The film of claim 2,wherein core layer (b) is from 7.5 to 70 μm thick and intermediate layer(c) is from 1 to 3 μm thick.
 11. The film of claim 2, wherein one orboth of an outer surface of first outer layer (a) and an outer surfaceof second outer layer (d) is surface-treated by a treatment selectedfrom the group consisting of corona discharge treatment, flametreatment, and plasma treatment.
 12. The film of claim 2, wherein anouter surface of first outer layer (a) has applied thereon a coatingselected from the group consisting of ethylene-acrylic acid copolymer(EAA), ethylene-methacrylic acid copolymer (EMA), alkyl acrylatecopolymer, acrylonitrile, polyvinylidene chloride (PVdC), polyvinylalcohol (PVOH), and urethane copolymer.
 13. The film of claim 2, whereina metal layer is coated on an outer surface of first outer layer (a) byvacuum metallization.
 14. The film of claim 2, wherein the film has aratio of plateau crimp seal strength to peak crimp seal strength ofgreater than 60% and less than 100%.
 15. The film of claim 2, whereincore layer (b) comprises from 1 wt % to 5 wt % of an ethylene-α-olefinelastomer as a supplemental component.
 16. A method of manufacturing thefilm of claim 2, comprising the steps of: (a) coextruding meltscorresponding to the thermoplastic polymer of first outer layer (a), thepeelable blend of core layer (b), the propylene homopolymer ofintermediate layer (c), and the thermoplastic polymer of sealable secondouter layer (d); (b) quenching the melts to form a coextruded sheet; and(c) biaxially orienting the coextruded sheet to form a sealable andpeelable film.
 17. An oriented sealable and peelable film, comprising:(a) a first outer layer comprising a thermoplastic polymer; (b) a corelayer comprising a peelable blend comprising (i) from 10-35 wt % ofethylene-α-olefin elastomer and (ii) from 90-65 wt % of propylenehomopolymer; and (c) a sealable second outer layer comprising athermoplastic polymer, wherein scalable second outer layer (c) ispositioned such that core layer (b) is between first outer layer (a) andsealable second outer layer (c).
 18. An oriented sealable and peelablefilm, comprising: (a) a first outer layer comprising a thermoplasticpolymer; (b) a core layer comprising a peelable blend comprising (i)from 10-35 wt % of ethylene-α-olefin elastomer and (ii) from 90-65 wt %of propylene homopolymer; (c) an intermediate layer comprising apropylene homopolymer, wherein intermediate layer (c) is positioned suchthat core layer (b) is between first outer layer (a) and intermediatelayer (c); and (d) a sealable second outer layer comprising athermoplastic polymer, wherein sealable second outer layer (d) ispositioned such that intermediate layer (c) is between core layer (b)and sealable second outer layer (d).
 19. The film of claim 18, whereinthe ethylene-α-olefin elastomer is an ethylene-propylene elastomer, andcore layer (b) comprises a peelable blend comprising (i) from 10-20 wt %of ethylene-propylene elastomer and (ii) from 90-80-wt % of propylenehomopolymer.